I have a 3 class GMM with continuous y's (4 time points) and 3 X's (and 100 random starts). When I test X1 and X2 the last class is the normative class, as expected, and the coefficients for C1 and C2 are relative to the normative class. However, when I test X3 (alone, without X1 and X2) the reference group changes so that the largest class (normative) is the first class is thus compared to the last class (which is now a non-normative class)--the class distributions stay essentially the same. I would like to report the results relative to the normative class, how might I change this in the command language? Thanks in advance.

You have to give some key starting values to make a certain class come last. For instance, take the estimates for the normative class in the solution where this comes last and use them as starting values for the last class in the new run.